System and method for establishing secure communication

ABSTRACT

A system and method is described in which two parties communicate a first shared random number and a second shared random number, and each independently use a combining function with inputs including the two shared random numbers to obtain a shared secret key. Secure communication of the shared random numbers is performed by using a password and an asymmetric key pair. The password and the private key are not communicated, thereby preventing eavesdroppers from obtaining information sufficient to determine the shared secret key. Direct attacks on the parties are foiled by preventing the password from being stored, not storing the private key, and using two shared random numbers in case one is compromised by an attack on one of the two parties. A party cannot be effectively impersonated without knowledge of the password, and a called party cannot be impersonated without additionally controlling the network.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to encoding systems and protocols, and more specifically to systems and protocols for establishing a shared secret key for two-way secure communications.

[0003] 2. Description of Related Art

[0004] When two parties wish to communicate securely, an efficient mechanism for doing so is the use of a shared secret session key, i.e., a key known only to the two parties that can be used symmetrically to both encrypt and decrypt messages between them for the duration of a communication session. Various methods exist to achieve this, and each have advantages and disadvantages.

[0005] Parties can use a trusted key authority that distributes the shared secret key to each of them separately using their unique key encryption key. However, this technique requires the storage of keys—i.e., it is not portable with a user, and if a key encryption key is compromised the system loses its integrity and past communications can be decrypted.

[0006] The “Diffie-Hellman” technique, described in U.S. Pat. No. 4,200,770, permits generation of a shared secret key without the use of encryption. Each party generates a large random number. By way of example, party A generates the number X and party B generates the number Y. Each party sends its number through a particular kind of one way function and transmits the output. Only knowledge of one number (X or Y), and the value of the other number sent through the one-way function is sufficient to generate the shared secret key. A drawback of the Diffie-Hellman technique is that each side uses a non-shared random number (X or Y) in independently generating the shared secret key. A result of the use of non-shared random numbers is that each side performs large exponential and modulo calculations when performing one-way functions and generating the shared secret key, resulting in a high computational load on both sides. These calculations are required in order to make it computationally infeasible for an eavesdropper to combine the two-shared numbers in order to obtain the shared secret key.

[0007] Variations on the Diffie-Hellman technique exist that attempt to make it more secure. These variations suffer from the same computational burden as the standard Diffie-Hellman technique. For example, U.S. Pat. No. 5,953,424 describes a system with a modification of the key generation technique. In addition to the usual Diffie-Hellman computations on the original numbers (X and Y) and the transmitted numbers (which result from calculations), the '424 patent describes extra factors that may be combined with the standard Diffie-Hellman factors. These factors are not transmitted, so they must be knowable in advance by the communicating parties.

[0008] Another variation of the Diffie-Hellman technique is disclosed in U.S. Pat. No. 5,440,635. In this variant, the transmitted numbers are further encrypted using a symmetric key cryptosystem before being transmitted. This doesn't ameliorate any of the disadvantages of Diffie-Hellman, noted above.

[0009] A message exchange technique employing a combination of public and private key cryptography to communicate a secret key from one party to another is described in U.S. Pat. No. 5,241,599. The '599 patent requires that each party share knowledge of a secret. A calling party generates a random public key/private key pair, and communicates the public key to the called party using their shared secret. The called party then communicates the secret key to the calling party using both the public key and the shared secret. The technique of the '599 patent suffers from several limitations. The calling party must generate a random public key/private key pair, which is a costly computation that is often preferably performed by the called party. Also, the secret key may be compromised in advance by manipulating the called party to affect the secret key it uses or computes. No manipulation or compromise of the calling party is required.

[0010] What is needed is a system and method for establishing secure communication.

SUMMARY OF THE INVENTION

[0011] It is an object of the present invention to provide an encoding protocol for communicating parties to each obtain a shared secret key.

[0012] One advantage of the present invention is that it is less computationally intensive than previous cryptographic systems to obtain a shared secret key.

[0013] Another advantage of the present invention is that the calling party is not required to perform any large computations.

[0014] Yet another advantage of the present invention is that it is highly resistant to attacks, including eavesdropping, impersonating a party, replay attacks, tampering with or probing a party before or after a communications session, and password database hijacking.

[0015] Still another advantage of the present invention is that it can be used either with or without certificates or physical tokens such as smart cards or biometric devices.

[0016] In a method for obtaining a shared secret key according to the present invention, a party identifies a first shared random number and a second shared random number, and obtains the shared secret key from an output of a combining function having a first input including the first shared random number and having a second input including the second shared random number.

[0017] In a further aspect of the present invention, the shared secret key is used to transform messages.

[0018] In another aspect of the present invention, a party encodes a first shared random number, decodes a second shared random number, and obtains the shared secret key from an output of a combining function having a first input including the first shared random number and having a second input including the second shared random number.

[0019] In a further aspect of the present invention, a party encodes a first shared random number and a second key using a first key obtained using information obtained from a password; decodes a second shared random number using a third key; and obtains the shared secret key from an output of a combining function having a first input including the first shared random number and having a second input including the second shared random number.

[0020] In a still further aspect of the present invention, the second key and the third key form an asymmetric key pair.

[0021] In another aspect of the present invention, a party decodes a first shared random number, encodes a second shared random number, and obtains the shared secret key from an output of a combining function having a first input including the first shared random number and having a second input including the second shared random number.

[0022] In a further aspect of the present invention, a party decodes a first shared random number and a second key using a first key obtained from information obtained from a password, encodes a second shared random number using the second key, and obtains the shared secret key from an output of a combining function having a first input including the first shared random number and having a second input including the second shared random number.

[0023] In another aspect of the present invention, a party communicates a first shared random number and a second shared random number, and obtains the shared secret key from an output of a combining function having a first input including the first shared random number and having a second input including the second shared random number.

[0024] In a further aspect of the present invention, the party communicates an asymmetric key and a timestamp with the first shared random number, and a timestamp with the second shared random number.

[0025] In still another aspect of the present invention, a device including at least one processor executes software instructions identifying a first shared random number and a second shared random number, and obtains the shared secret key from an output of a combining function having a first input including said first shared random number and having a second input including said second shared random number.

[0026] In yet another aspect of the present invention, a machine-readable storage medium contains instructions for a processor, including encoded computer means for identifying a first random number, encoded computer means for identifying a second random number, and encoded computer means for obtaining the shared secret key from an output of a combining function having a first input including said first shared random number and having a second input including said second shared random number.

BRIEF DESCRIPTION OF THE DRAWINGS

[0027]FIG. 1a illustrates a peer-to-peer embodiment of the present invention, including various embodiments of each peer.

[0028]FIG. 1b illustrates a client-server embodiment of the present invention, including various embodiments of a client.

[0029]FIG. 2 illustrates a sequence of operations performed by a peer, a client, or a server according to the present invention.

[0030]FIG. 3 illustrates a sequence of operations performed by a calling party in a peer-to-peer embodiment, or a client in a client-server embodiment of the present invention.

[0031]FIG. 4 illustrates a sequence of operations performed by a called party in a peer-to-peer embodiment, or a server in a client-server embodiment of the present invention.

[0032]FIG. 5 illustrates a packet that may be used in a signal embodiment of the present invention.

[0033]FIG. 6 illustrates a sequence of actions and communications among a user, a calling party, and a called party in one embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0034] The present invention provides a system and method for two parties to determine a shared secret key. Each party identifies a first shared random number and a second shared random number. Then, a combining function is used to obtain a shared secret key using the first shared random number and the second shared random number. Hence, knowledge of the combining function coupled with knowledge of the first shared random number and the second shared random number is sufficient to obtain the shared secret key. It is preferred, therefore, for the shared random numbers to be communicated between the parties without permitting would-be attackers to learn both shared random numbers. In some embodiments, this is accomplished by using a password. Specifically, each party has access to either information obtained from a password, or of the password itself. In a preferred embodiment, the password is associated with a user.

[0035] A shared secret key may be used along with a symmetric encryption system such as IDEA (International Data Encryption Algorithm) in order to efficiently and securely perform communications between two parties. It is desirable that the shared secret key be secure and that the two parties authenticate each other, while minimizing the computational load necessary to obtain the shared secret key.

[0036] The system and method of the present invention can be implemented in a local area network, wide area network, public access network (e.g., Internet), in a network of networks such as a hybrid network, or in other communication environments as would be apparent. In a network implementation that conforms to the OSI model, the shared secret key may be viewed as a session key. In an OSI-compliant embodiment, the protocol of the present invention for obtaining a shared secret key resides at layers 5 and/or 6 of the OSI model, and supports secret key based encoded transport of any developer-defined or selected client-server or peer-to-peer protocol. In addition, a user authentication graphical user interface (GUI) for any developer-defined applications may be provided above the protocol of the present invention, as would be apparent. In addition, the protocol of the present invention may be encapsulated within another protocol such as a firewall, a virtual private network, or both, or any other protocol as would be apparent. With encapsulation, an application benefiting from the authentication and encoded transport of the present invention does not need to be aware of the details or even the existence of the underlying protocol of the present invention.

[0037] In generating a shared secret key according to some embodiments, the system and method of the present invention provides a secure and robust user authentication protocol, based on asymmetric key encoding. In a preferred embodiment, a first party communicates a public key to a second party using information obtained from a password associated with a user of the second party. The first and second parties exchange shared secret keys which no outside observer can obtain without information about the password and information about a private key associated with the public key, which is not communicated.

[0038]FIG. 1a and FIG. 1b depict exemplary embodiments of the environment of the present invention. FIG. 1a shows an exemplary peer-to-peer embodiment. Users 101 a through 101 e and 105 a through 105 e are graphically depicted as human users for ease of representation, although they may be automated entities such as applications, daemons, or other electronically-driven users. A user need not be associated with a particular human if it is a non-human user such as a software-driven user, although it can be. Calling users 101 communicate with (i.e., are connected to) exemplary calling platforms 102 a through 102 d, and called users 105 communicate with exemplary called platforms 104 a through 104 d.

[0039] The term ‘party’ may refer to a user, a platform, or both a user and a platform with which the user is associated. In one embodiment, a calling party is a party that initiates a communications session; and a called party is a party that responds to a calling party's initiation of a communications session. Network 103 represents any network or network of networks, such as the Internet, and may include firewalls, virtual private networks, and any kinds of connections (e.g., wireless, Ethernet, etc.), routers, gateways, protocols, and other components as would be apparent. Exemplary platforms 102 a and 104 a represent laptop computers, which may be connected to network 103 via wire-line or wireless connections, as would be apparent. Exemplary platforms 102 b and 104 b represent workstations or personal computers. Exemplary platforms 102 c and 104 c represent handheld devices. Exemplary platforms 102 d and 104 d represent servers, which may be better equipped than the other exemplary platforms to handle simultaneous connections to multiple users including remote users, as illustrated. Other platforms may be used, such as a dumb terminal, as would be apparent. For the purposes of this specification, a platform may comprise one or more pieces of hardware, a process running on the hardware, a process in memory or storage, or a combination thereof. For example, platform 104 d may represent the physical server, i.e., the hardware comprising the server. Alternatively, platform 104 d may represent a server process running on the server or in memory on the server. As an additional alternative, platform 104 d may represent a combination of these things. A non-human user may be running at least partially on a platform with which it is associated, or it may be running completely remotely. The meaning of platform varies throughout the specification, and is in each case subject to any of the interpretations just enumerated.

[0040]FIG. 1a depicts a peer-to-peer configuration, in which a party (possibly including one of exemplary users 101 a through 101 e and/or one of corresponding exemplary platforms 102 a through 102 d) may be either a calling party or a called party. Similarly, any of exemplary users 105 a through 105 e and/or a corresponding exemplary platform 104 a through 104 d, could be either a calling or a called party. FIG. 1b represents a client-server configuration in which a client (possibly including one of exemplary users 101 a through 101 e and/or one of corresponding exemplary platforms 102 a through 102 d) is the calling party and a party on the server side, including user 105 d and/or server platform 104 d is the called party 105 d. The present invention may be used to connect parties, including a calling party and a called party to provide for authentication and/or secure communication between the calling party and the called party, through network 103.

[0041] A random number has the property that it is difficult for a would-be attacker to determine the random number without obtaining information characterizing the random number. A random number that is either communicated or intended to be communicated between a calling party and a called party is referred to as a shared random number. In order to communicate a shared random number, a party may send or receive the shared random number or information from which the shared random number may be obtained without additional information specific to the shared random number and without an astronomical number of computations. A shared random number may be sent or received by transmitting or receiving over a communications channel or a network information from which the shared random number may be easily inferred, such as the shared random number itself.

[0042] The present invention employs at least two shared random numbers to obtain a shared secret key. The shared random numbers are passed through a combining function to obtain information used to determine the shared secret key. A combining function may be any function, including a compound function, i.e., a function of functions, that has a first input including a first number and a second input including a second number. Additionally, a combining function has the property that knowledge of a single input to the combining function does not substantially reduce the difficulty of determining an output of the combining function. It is preferred that a combining function be used such that knowledge of a single input to the combining function does not reduce the difficulty of determining an output of the combining function at all.

[0043] A benefit of passing shared random numbers through a combining function to obtain a shared secret key is that a would-be attacker will be unable to compromise the shared secret key by obtaining only one random number, either through observation or manipulation of a party or its communications, even with knowledge of the protocols used and the combining function itself. A combining function may involve one or more of a number of operations on its inputs and any parameters that might be inherent to the combining function. For example, addition, subtraction, multiplication, division, exponentiation, logarithms, trigonometric functions, and/or modulo operations could be used. A combining function could include a logical function, such as OR, AND, NOR, NAND, XOR, and/or XNOR, blending or merging (scaling, and then addition), bit shifting, concatenation, truncation, or any combinations thereof. Additional operations, conditional operations, and various combinations of operations, in serial and/or parallel may be used, as would be apparent. In a preferred embodiment, an XOR operation is used, which would permit the use of a combining function as simple as specifying an output of a combining function to be equal to an XOR of two inputs.

[0044]FIG. 2 illustrates a set of steps performed by a party in an embodiment of the present invention. In step 201, the party shares a first random number R1. The random number could be shared by being communicated to or from another party, possibly through intermediaries. In step 202, the party shares a second random number R2. In step 203, the party obtains an output K of a combining function f() with a first input including R1 and a second input including R2. In FIGS. 2-4, for ease of presentation, an exemplary embodiment of the combining function is shown with two inputs consisting of R1 and R2, respectively, yielding K=f(R1,R2).

[0045]FIG. 3 illustrates a set of steps performed by a calling party in an embodiment of the present invention. In a client-server embodiment, FIG. 3 illustrates a set of steps performed by a client. For ease of description, the party executing the steps in FIG. 3 will be referred to as a ‘calling party,’ which encompasses the term ‘client.’ In step 301, the calling party receives a first shared random number R1. In step 302, the calling party sends a second shared random number R2. In step 203, the calling party obtains an output K of a combining function f( ) with a first input including R1 and a second input including R2.

[0046]FIG. 4 illustrates a set of steps performed by a called party in an embodiment of the present invention. In a client-server embodiment, FIG. 4 illustrates a set of steps performed by a server. For ease of description, the party executing the steps in FIG. 4 will be referred to as a ‘called party,’ which encompasses the term ‘server.’ In step 401, the called party sends a first shared random number R1. In step 402, the called party sends a second shared random number R2. In step 203, the called party obtains an output K of a combining function f() with a first input including R1 and a second input including R2.

[0047] When a party communicates information, it may do so over network 103. In order to send information, the information may be encoded to comply with a communications protocol. It may further be encoded with keys, passwords, or information derived therefrom. Encoding with keys or passwords or information derived therefrom may comprise encryption, or other forms of transforming data as would be apparent. If information is sent through network 103, it may be encoded in packets, such as IP packets. An exemplary IP packet is illustrated in FIG. 5. The IP packet of FIG. 5 includes an IP header 501 including a source address 502 and a destination address 503, and embedded data 504 including part of the information sent through the network. When a party receives information through network 103, it may decode information according to a network protocol, such as the Internet Protocol. Information may be decoded with keys or passwords or information derived therefrom. Decoding with keys or passwords or information derived therefrom may comprise decryption. Decoding of information may also comprise parsing, in which information is extracted from data passed through a network, such as a packet or packets.

[0048] Information communicated over network 103 is propagated through network 103 between communicating parties. Networks may comprise many kinds of links, including wireless links. Signals sent over the network may be embedded in a carrier wave, and may be propagated, e.g., as an analog or a digital signal.

[0049] If keys or passwords, including information derived from them are used to encode or decode information, then a key or password may itself be encoded. In one embodiment, a password is encoded to obtain a 128-bit key. One method of performing this encoding is as follows. In a first step, 1case is used to transform all alphabetic characters to lower-case. In a second step, characters are transformed based on a stored table. In a third step, all bits in the transformed representation of each character are concatenated. In a fourth step, the resulting bit stream is repeated until the total bit length is 128. In a fifth step, IDEA is used to encrypt the original password using the 128-bit stream as the secret key. In a sixth step, the cyphertext is padded to create a 128-bit key, which may be used to encode and/or decode information.

[0050] The above method for encoding a password is an example of using a one-way function. A one-way function has the property that it is computationally infeasible to determine an input to the function by using an output of the function. The six-step method for encoding the password is equivalent to passing the password through a function. In this case, it is a one-way function because the encrypting step makes it computationally infeasible to recover the input by using the output. Another example of a one-way function is a hash.

[0051]FIG. 6 illustrates a preferred embodiment of the present invention. The four columns of the figure represent users and platforms. Specifically, column 101 represents a calling party, column 102 represents a calling platform, column 104 represents a called platform, and column 105 represents a called user. Calling user 101 is connected to calling platform 102, and called user 105 is connected to called platform 104. Arrows represent messages sent between the four entities (columns) in FIG. 6, and numbers without arrows represent operations that may be performed by either or both of the adjacent columns. For example, step 601 represents a message sent from calling user 101 to calling platform 102, and step 604 represents a step that may be performed by called platform 104, called user 105, or both.

[0052] In step 601, calling user 101 sends user identification information (User ID) and a password to calling platform 102. The password does not need to be placed in storage on calling platform 102, and could be held in memory on platform 102 just long enough for it to fulfil its use. If calling user 101 is a human user, the action of sending the User ID and password to platform 102 could be triggered by the action of the human user typing in the User ID and password on a keyboard or other alphanumeric input device. In step 602, calling platform 102 sends information to called platform 104 including information obtained from the User ID and information concerning a protocol and version that calling platform 102 is capable of using.

[0053] Step 603 is carried out by the calling party, which may comprise calling user 101, calling platform 102, or both. In step 603, a first key, denoted K_(user), is generated using information obtained from the password. In some embodiments, the first key is generated as an output of a one way function having an input including the password. In other embodiments, other methods of encoding the password may be used to obtain K_(user). Other methods may be used to obtain K_(user), as would be apparent.

[0054] Steps 604 through 606 are carried out by the called party, which may comprise called platform 104, called user 105, or both. In step 604, the called party identifies a first shared random number R1. This and other identification steps could comprise, for example, generating R1, looking up R1 in a table, obtaining R1 from an external source, and/or other methods as would be apparent. In step 605, the called party identifies an asymmetric key pair comprising two corresponding asymmetric keys, e.g., a public key and a private key. For ease of representation, the two asymmetric keys are denoted K_(public) and K_(private).

[0055] In step 606, a first key, K_(user), is obtained by using information obtained from the User ID. In some client-server embodiments, the first key is obtained by performing a table lookup using information obtained from the User ID. For example, one embodiment that uses a first key comprising an encoded password requires the called party to have access to a table of passwords, which are indexed by User ID. In this way, step 606 may be performed by looking up the password in the password table using the User ID or information obtained therefrom, and sending the password through a one-way function to obtain the first key. Alternatively, the password table may contain encrypted or encoded passwords, and a simple table lookup may be used to obtain the first key without an extra encoding step. In another embodiment, the password table is itself encoded. The table could be encoded as a whole, or it could be broken into sub-tables or fields, with each sub-table or field encoded separately. If the password table is encoded, the called party may decode the table or a relevant part of it as part of step 606.

[0056] Step 606 may be performed in other ways. For example, in some embodiments including a peer-to-peer embodiment, information obtained from the User ID is used to obtain from a trusted third party either the first key or information used to generate the first key.

[0057] In step 607, the called party sends the calling party a first message encoded with the first key, K_(user). The first message includes the first shared random number, R1, and one of the two asymmetric keys identified in step 605, which we arbitrarily denote K_(public). The first message also includes a timestamp in some embodiments, although in a preferred embodiment timestamps are not used because of timing sychronization issues. The first message may be denoted K_(user)(R1,K_(public),timestamp).

[0058] Steps 608 and 609 are performed by the calling party, comprising the calling user 101 and/or the calling platform 102. In step 608, the first message is decoded. In order to decode the first message, the calling party uses K_(user). Then, R1 and K_(public) are obtained from the first message. One method to obtain R1 and K_(public) from the first message is to parse the message, including any header information that may exist. If the first message includes a timestamp, then it may be obtained from the first message and compared to the actual time. In step 609, a second shared random number R2 is identified.

[0059] In step 610, the calling party sends the called party a second message encoded with the asymmetric key K_(public). The second message contains the second shared random number R2. The second message also includes a timestamp in some embodiments, although in a preferred embodiment timestamps are not used because of time synchronization issues. The second message may be denoted K_(public)(R2,timestamp).

[0060] Step 611 is carried out by the called party. In step 611, the second message is decoded using the other asymmetric key, K_(private), to obtain R2. One method to obtain R2 from the second message is to parse the message, including any header information that may exist. If the second message includes a timestamp, then it may be obtained from the second message and compared to the actual time.

[0061] Step 612 is carried out both by the calling party and by the called party. In step 612, the shared secret key, K_(ss), is obtained from an output of a combining function having a first input including the first shared random number and a second input including the second shared random number. In one embodiment, the shared secret key is the output of a combining function having two inputs consisting of the two shared random numbers. This is denoted by K_(ss)=f(R1,R2).

[0062] In step 613, the two parties communicate using K_(ss). K_(ss) may be used, e.g., in any symmetric encryption system to transform messages. A sender of a message transforms the message by encoding it using K_(ss), and a receiver of a message transforms the message by decoding it using K_(ss).

[0063] The present invention may be used with client/server and peer-to-peer embodiments. In a peer-to-peer architecture, the called party could also pre-generate keys. A problem with peer-to-peer is that password management becomes difficult because there is no centralized repository. Because password information is extremely sensitive, passing passwords becomes a challenge.

[0064] Use of the present invention accrues numerous benefits. One benefit is that there is no need to use certificates. Therefore, there is no need to register with Certificate Authorities and keep them up to date. This removes an external source of unnecessary problems—a Certificate Authority's errors. Furthermore, if a user wishes to log in to a server using a client-server embodiment of the present invention, then any computer logged in to (i.e., used as a client) can immediately have access without ensuring that the computer has been registered with a certificate authority.

[0065] Another benefit of the present invention is that in some embodiments keys are not stored on local computers. In embodiments in which keys are generated dynamically, keys never need to be stored on a filesystem. Storing keys on the system allows someone who is capable of compromising a computer to steal the keys, and decrypt messages past, present, or future. In some embodiments of the present invention, keys are constantly changed and never stored on a computer's hard drive.

[0066] Yet another benefit of the present invention is that it is not necessary for a calling party to generate keys. Generating asymmetric key pairs can be computationally expensive, resulting in system delays. A calling party may have access only to limited computational resources. If an asymmetric key pair is generated on a limited machine, connection times between 15 seconds and nearly 2 minutes are typical using current hardware and algorithms. As keys take more computing power to generate, which is likely because the requirements of key size will increase, the present invention will allow a quick logon time from a computationally limited calling party. In some client-server embodiments, a server may generate keys constantly (i.e., semi-dynamically). Semi-dynamic key generation in a client-server embodiment allows connection latency to be independent of client and server hardware requirements.

[0067] Still another benefit of the present invention is that human users don't need to bring anything with them when connecting to another party in a peer-to-peer embodiment or logging on in a client-server embodiment. All that a human user needs to supply is a password. There is no need for a human user to carry a floppy disk with his or her stored “authorized key pair,” which reduces the potential for human error, e.g., an administrator emailing a key pair to a human user. Also, there is no need for a human user to have a physical token to log on. This enables true mobility by preventing the need for hardware such as a SmartCard reader.

[0068] A security benefit of the present invention comes from the double integrity of the shared secret key. In the present invention, the shared secret key is not sent in a single message. The shared secret key is computed based on the values of two shared random numbers. The first shared random number is encoded using a function based on the password. The second shared random number is encoded using a random public key. So even if someone were able to somehow steal a user's password, he still would have no way to decrypt the messages that the user had transmitted in the past. Secure data remains secure.

[0069] The double integrity of the shared secret key adds another benefit: if an attacker is able to penetrate a party and manipulate it prior to or during a communications session, it might in this way be able to weaken, sabotage, specify, or intercept a shared random number. However, without the other shared random number, the attack would not yield the shared secret key. No attack that targets only one shared random number can weaken the shared secret key.

[0070] The present invention provides strong security protection in obtaining a shared secret key. The following are some examples of attacks that are thwarted by the system and method of the present invention:

[0071] No password eavesdropping

[0072] No form of the password is ever sent, so one could never obtain the password.

[0073] No password database hijacking

[0074] The password database itself is encrypted, so one would never be able to grab any form of the password, to launch an off-line password guessing attack.

[0075] No reflection (man-in-the-middle) attack

[0076] At no point can a message be pulled from one authentication session, and used sensibly in a different session, to obtain access to keys or messages.

[0077] No replay attack

[0078] Because of the use of timestamps in some embodiments of the present invention, it is not possible to use untampered messages to cause either party to undergo processing that would ordinarily prohibit a valid user from gaining access to the system.

[0079] No impersonating called party

[0080] Impersonating the server would never gain an impersonator access to a password, because no form of the password is ever sent by the calling party. (The called party uses a function of the password as a key.). For this matter, it would never make sense for an attacker to impersonate the called party.

[0081] The specific algorithms and steps described herein, as well as the basic steps which such algorithms represent (even if they are replaced by different algorithms), are designed for implementation using general purpose microprocessors. Furthermore, each of the algorithms and steps described herein, as well as the basic steps represented by such algorithms, can be encoded on computer storage media such as CD ROMS, floppy disks, computer hard drives, and other magnetic, optical, other machine readable media, whether alone or in combination with one or more of the algorithms and steps described herein.

[0082] Although the methods discussed herein have been described in detail with regard to some exemplary embodiments and drawings thereof, it should be apparent to those skilled in the art that various adaptations and modifications of the methods can be accomplished without departing from the spirit and the scope of the invention. Thus, by way of example and not of limitation, the methods are discussed as illustrated by the figures. Accordingly, the invention is not limited to the precise embodiments shown in the drawings and described in detail hereinabove, but is set out in the following claims. 

What is claimed
 1. A method for obtaining a shared secret key, comprising the steps of: identifying a first shared random number; identifying a second shared random number; and obtaining the shared secret key from an output of a combining function having a first input including said first shared random number and having a second input including said second shared random number.
 2. The method of claim 1, wherein said combining function includes a logical function.
 3. The method of claim 2, wherein said logical function includes an exclusive or (XOR) function.
 4. A method for obtaining a shared secret key utilized in a network having at least a first computer and a second computer, said method comprising the steps of: transmitting a first message from said first computer to said second computer, said first message including a first shared random number; generating a second shared random number in said second computer; and generating a shared secret key from an output of a combining function having a first input including said first shared random number and having a second input including said second shared random number.
 5. The method of claim 4, further comprising the step of transmitting a second message from said second computer to said first computer, said second message including said second shared random number.
 6. The method of claim 5, wherein said first message is encoded using an encoded password.
 7. The method of claim 6, wherein said encoded password is an encrypted password.
 8. The method of claim 6, wherein said step of encoding said first message comprises encrypting said first message using said encoded password.
 9. The method of claim 5, wherein said first message also includes an asymmetric key.
 10. The method of claim 9, wherein said second message is encoded using said asymmetric key.
 11. The method of claim 10, wherein said second message is encrypted using said asymmetric key.
 12. The method of claim 5, wherein said combining function includes a logical function.
 13. The method of claim 12, wherein said logical function includes an exclusive or (XOR) function.
 14. An electronic data signal including information encoded using a shared secret key, wherein said shared secret key is obtained from an output of a combining function having a first input including said first shared random number and having a second input including said second shared random number.
 15. The data signal of claim 13, wherein said data signal is propagated through a network.
 16. The data signal of claim 13, wherein said information is encoded using said shared secret key.
 17. The data signal of claim 15, wherein said information is encrypted using said shared secret key.
 18. The signal of claim 13, wherein said signal comprises a packet of data representing a portion of said information.
 19. The signal of claim 13, wherein said signal is a wireless signal.
 20. The signal of claim 13, wherein said signal is embedded in a carrier wave.
 21. The signal of claim 13, wherein said signal is propagated as an analog signal.
 22. The signal of claim 13, wherein said signal is propagated as a digital signal.
 23. The signal of claim 13, wherein said combining function includes a logical function.
 24. The method of claim 22, wherein said logical function includes an exclusive or (XOR) function.
 25. A method for obtaining a shared secret key, comprising the steps of: receiving a first message including a first shared random number; identifying a second shared random number; obtaining the shared secret key from an output of a combining function having a first input including said first shared random number and having a second input including said second shared random number.
 26. The method of claim 24, further comprising the step of transmitting a second message including said second shared random number.
 27. The method of claim 25, wherein said step of identifying a second shared random number comprises generating said second shared random number.
 28. The method of claim 25, wherein said first message is encoded using a first key obtained using information obtained from a password.
 29. The method of claim 27, wherein said first message is encoded using a first key obtained using information obtained from a password.
 30. The method of claim 28, wherein said first message is encrypted using a first key obtained using information obtained from a password.
 31. The method of claim 27, wherein said first key is obtained by encoding said password.
 32. The method of claim 30, wherein said step of encoding said password comprises encrypting said password.
 33. The method of claim 27, wherein said first message also includes a second key.
 34. The method of claim 32, wherein said second key is an asymmetric key.
 35. The method of claim 32, wherein said second message is encoded with said second key.
 36. The method of claim 34, wherein said second message is encrypted with said second key.
 37. The method of claim 32, further comprising receiving said password from a user.
 38. The method of claim 24, wherein said combining function includes a logical function.
 39. The method of claim 24, wherein said logical function includes an exclusive or (XOR) function.
 40. The method of claim 27, wherein said first key is generated using an encoded password obtained from said password.
 41. The method of claim 39, wherein said encoded password is an encrypted password.
 42. The method of claim 40, wherein said encrypted password is obtained from an output of a one-way function having an input including said password.
 43. The method of claim 41, wherein said one-way function is a hash function.
 44. The method of claim 27, further comprising the step of receiving said password from a user.
 45. The method of claim 43, further comprising transmitting information identifying said user.
 46. The method of claim 43, wherein said user is a human user.
 47. The method of claim 43, further comprising the step of obtaining said first key from an output of a one-way function having an input including said password.
 48. The method of claim 43, further comprising decrypting said first message using information obtained from said password.
 49. Otto The method of claim 27, further comprising transmitting identification information for a user.
 50. The method of claim 27, wherein said first message also includes a second key.
 51. The method of claim 49, wherein said second key is an asymmetric key.
 52. The method of claim 50, wherein said second message is encoded with said second key.
 53. The method of claim 37, wherein said second message is encrypted with said second key.
 54. The method of claim 51, wherein said second message also includes a timestamp.
 55. The method of claim 27, wherein said first message also includes a timestamp.
 56. The method of claim 27, wherein said first message also includes a second key and a timestamp.
 57. The method of claim 55, wherein said second key is an asymmetric key.
 58. A device including at least one processor, said at least one processor executing software instructions for obtaining a shared secret key, said software instructions comprising a software module identifying a first shared random number and a second shared random number and obtaining the shared secret keybased on said first shared random number and said second shared random number, wherein the device is capable of transforming messages using the shared secret key.
 59. The device of claim 57, wherein the first shared random number is communicated to a user.
 60. The device of claim 58, wherein the shared secret key is obtained from said user.
 61. The device of claim 57, wherein the shared secret key is obtained from an output of a combining function having a first input including said first shared random number and having a second input including said second shared random number.
 62. The method of claim 60, wherein said step of identifying a first shared random number comprises generating said first shared random number.
 63. The method of claim 61, wherein said step of identifying a second shared random number comprises receiving a second message including said second shared random number.
 64. The method of claim 60, wherein said step of identifying a second shared random number comprises generating said second shared random number.
 65. The method of claim 63, wherein said step of identifying a first shared random number comprises receiving a first message including said first shared random number.
 66. The device of claim 60, wherein said device is capable of transforming messages by encoding messages using the shared secret key.
 67. The device of claim 65, wherein said encoding messages using the shared secret key comprises encrypting messages using the shared secret key.
 68. The device of claim 60, wherein said device is capable of transforming messages by decoding messages using the shared secret key.
 69. The device of claim 67, wherein said decoding messages using the shared secret key comprises decrypting messages using the shared secret key.
 70. The device of claim 60, wherein said device comprises a computer.
 71. The device of claim 60, wherein said device comprises a handheld device.
 72. The device of claim 60, further comprising a memory coupled to said processor, wherein at least a portion of said software module is stored in said memory.
 73. A device including at least one processor, said at least one processor executing software instructions for obtaining a shared secret key, said software instructions comprising a software module parsing a first message including a first shared random number to identify said first shared random number, identifying a second shared random number, and obtaining the shared secret key from an output of a combining function having a first input including said first shared random number and having a second input including said second shared random number, wherein the shared secret key is used by the device to transform messages.
 74. The device of claim 72, wherein said device decrypts said first message.
 75. The method of claim 72, wherein said step of identifying a second shared random number comprises generating said second shared random number.
 76. The device of claim 72, wherein said device transmits a second message including the second shared random number.
 77. The device of claim 75, wherein said first message is encoded using a first key obtained using information obtained from a password.
 78. The device of claim 76, wherein said first message is encrypted using a first key obtained using information obtained from a password.
 79. The device of claim 76, wherein said first message also includes an asymmetric key.
 80. The device of claim 78, wherein said second message is encoded with said asymmetric key.
 81. The device of claim 79, wherein said second message is encrypted with said asymmetric key.
 82. A device including at least one processor, said at least one processor executing software instructions for obtaining a shared secret key, said software instructions comprising a first software module identifying a first shared random number, parsing a second message including a second shared random number to identify said second shared random number, and obtaining the shared secret key from an output of a combining function having a first input including said first shared random number and having a second input including said second shared random number, wherein the shared secret key is used by the device to transform messages.
 83. The device of claim 81, wherein said device decrypts said second message.
 84. The method of claim 81, wherein said step of identifying a first shared random number comprises generating said first shared random number.
 85. The device of claim 81, wherein said software module generates a first message including said first shared random number.
 86. The device of claim 84, wherein said first message also includes a second key.
 87. The device of claim 85, wherein said first message also includes an asymmetric key.
 88. The device of claim 86, wherein said second message is encoded with said asymmetric key.
 89. The device of claim 87, wherein said second message is encrypted with said asymmetric key.
 90. The device of claim 85, wherein said first key corresponds to a password known by a user.
 91. A machine-readable storage medium containing instructions for a processor, said instructions being the steps for the processor, comprising: encoded computer means for identifying a first shared random number; encoded computer means for identifying a second shared random number; and encoded computer means for obtaining the shared secret key from an output of a combining function having a first input including said first shared random number and having a second input including said second shared random number.
 92. A storage medium according to claim 90 wherein said storage medium is at least one of a group including semiconductor memory device, magnetic device, optical device, magneto-optical device, floppy diskette, hard drive, CD-ROM, magnetic tape, computer memory, and memory card.
 93. A storage medium according to claim 90, wherein said combining function includes a logical function.
 94. A storage medium according to claim 92 wherein said logical function includes an exclusive or (XOR) function.
 95. A machine-readable storage medium containing instructions for a processor, said instructions being the steps for the processor, comprising: encoded computer means for parsing a first message including a first shared random number to obtain said first shared random number; encoded computer means for identifying a second shared random number; and encoded computer means for obtaining the shared secret key from an output of a combining function having a first input including said first shared random number and having a second input including said second shared random number.
 96. The storage medium of claim 94, further comprising encoded computer means for decrypting said first message.
 97. The storage medium of claim 94, further comprising encoded computer means for generating a second message including said second shared random number.
 98. The storage medium of claim 96, wherein said first message is encoded using a first key obtained using information obtained from a password.
 99. The storage medium of claim 97, wherein said first message is encrypted using a first key obtained using information obtained from a password.
 100. The storage medium of claim 97, wherein said first message also includes an asymmetric key.
 101. The storage medium of claim 99, wherein said second message is encoded with said asymmetric key.
 102. The storage medium of claim 100, wherein said second message is encrypted with said asymmetric key.
 103. A machine-readable storage medium containing instructions for a processor, said instructions being the steps for the processor, comprising: encoded computer means for identifying a first shared random number; encoded computer means for parsing a second message including a second shared random number to obtain said second shared random number; and encoded computer means for obtaining the shared secret key from an output of a combining function having a first input including said first shared random number and having a second input including said second shared random number.
 104. The storage medium of claim 102, further comprising encoded computer means for decrypting said second message.
 105. The storage medium of claim 102, further comprising encoded computer means for transmitting a first message including said first shared random number.
 106. The storage medium of claim 104, wherein said first message also includes a second key.
 107. The storage medium of claim 105, wherein said second key is an asymmetric key.
 108. The storage medium of claim 106, wherein said second message is encoded with said asymmetric key.
 109. The storage medium of claim 107, wherein said second message is encrypted with said asymmetric key.
 110. The storage medium of claim 105, wherein said first message is encoded using a first key.
 111. The storage medium of claim 109, wherein said first message is encrypted using a first key.
 112. The storage medium of claim 109, wherein said first key corresponds to a password known by a user.
 113. A method for obtaining a shared secret key, comprising the steps of: identifying a first shared random number; receiving a second message including a second shared random number; and obtaining the shared secret key from an output of a combining function having a first input including said first shared random number and having a second input including said second shared random number.
 114. The method of claim 112, further comprising the step of transmitting a first message including said first shared random number.
 115. The method of claim 113, wherein said step of identifying a first shared random number comprises generating said first shared random number.
 116. The method of claim 113, wherein said first message is encoded using a first key.
 117. The method of claim 115, wherein said first message is encrypted using a first key.
 118. The method of claim 115, wherein said first message also includes a second key.
 119. The method of claim 115, wherein said first key corresponds to a password.
 120. The method of claim 118, wherein said first key is an encoded password.
 121. The method of claim 119, wherein said first key is an encrypted password.
 122. The method of claim 118, wherein said step of obtaining the shared secret key comprises obtaining the shared secret key from an output of a combining function having a first input including said first shared random number and having a second input including said second shared random number.
 123. The method of claim 121, wherein said combining function includes a logical function.
 124. The method of claim 122, wherein said logical function includes an exclusive or (XOR) function.
 125. The method of claim 117, wherein said second key is an asymmetric key.
 126. The method of claim 117, wherein said second message is encoded with said second key.
 127. The method of claim 125, wherein said second message is encrypted with said second key.
 128. The method of claim 125, further comprising decoding said second message.
 129. The method of claim 127, wherein said decoding said second message comprises decoding said second message using a third key.
 130. The method of claim 128, wherein said third key and said second key form an asymmetric key pair.
 131. The method of claim 129, further comprising the step of generating said asymmetric key pair.
 132. The method of claim 130, wherein said asymmetric key pair is generated dynamically.
 133. The method of claim 130, wherein said asymmetric key pair is selected from a set of pre-generated asymmetric key pairs.
 134. The method of claim 115, further comprising receiving information identifying a user.
 135. The method of claim 133, wherein said first key is associated with said user.
 136. The method of claim 134, wherein said first key corresponds to a password known by said user.
 137. The method of claim 135, wherein said first key is an encoded value of said password.
 138. The method of claim 135, wherein said encoded value of said password is an encrypted value of said password.
 139. The method of claim 136, wherein said first key is a value of said password after being sent through a one-way function.
 140. The method of claim 136, further comprising the step of obtaining said first key by looking up said user in a password file.
 141. The method of claim 139, wherein said password file contains an encoded password.
 142. The method of claim 140, wherein said encoded password is an encrypted password.
 143. The method of claim 139, wherein said password file is encoded.
 144. The method of claim 142, wherein said encoded password file is an encrypted password file.
 145. The method of claim 115, wherein said first message also includes a second key.
 146. The method of claim 144, wherein said second key is an asymmetric key.
 147. The method of claim 145, wherein said second message is encoded with said second key.
 148. The method of claim 146, wherein said second message is encrypted with said second key.
 149. The method of claim 146, wherein said second message also includes a timestamp.
 150. The method of claim 115, wherein said first message also includes a timestamp.
 151. The method of claim 115, wherein said first message also includes a second key and a timestamp.
 152. The method of claim 150, wherein said second key is an asymmetric key. 